In the water draining device of the existing bathtubs, cool water would leave in the pipe and the shower head end and the spraying shower end connected to the switch valve, therefore, when the user is getting a shower, cool water would be going to the human being that he may get ill, the water draining device is bad in comfort. If the user gets cool water draining first, he needs to stay beside the shower head to get shower after the cool water is drained out. This is a waste of time and labor, it is bad in user experience. If there is a cool water draining device that it opens to automatically drain cool water out and automatically closes after the cool water is drained out, the user doesn't need to stay beside the shower head when draining cool water out, the user can also operate the shower head to get the warm water, the user experience can be efficiently improved.